The determination of the position and orientation of an object in space is a problem relating to numerous technical fields. The various solutions generally afforded must have the principal characteristics of resolving any ambiguity in position or orientation, of responding to more or less severe dynamics of the systems and of satisfying high accuracy.
These systems are used in aeronautics, for detecting head posture, notably for the helmets of fighter aircraft, of military, civilian or para-civilian helicopters. They are also used for detecting simulation helmets, this detection can then be combined with an oculometry device, also called an eyetracker, for detecting position of the gaze. Numerous applications of these systems also exist in the field of virtual reality and games.
Currently, optical systems for detecting posture rely on two main principles. Firstly, it is possible to identify on an image, produced by a matrix sensor for example, the position of luminous pointlike emitters. Electroluminescent diodes, also called LEDs, can be used as emitters. Additionally, another solution consists in observing an unambiguous pattern printed on the object whose position and orientation are to be determined. For this purpose, one or more cameras are used to observe this pattern and analyze it on the basis of the images collected.
In the case of the use of luminous sources of the LED type, the latter are disposed in groups. These groups of LEDs are also called clusters. In the case of aeronautical applications, these clusters, disposed on the helmet, are generally not contained in a plane, and in numerous cases take the form of a tetrahedron on the helmet.
FIG. 1 represents a helmet 1 used in aeronautics for systems for detecting the position and orientation of objects in space. The diodes 10 placed on the helmet form a tetrahedron-shaped cluster. The tetrahedron is indicated by dashed lines in FIG. 1. This type of system requires sensors, generally cameras placed in the cockpit. This entails a multi-emitter/multi-receiver device whose emitters are the diodes and the receivers the cameras.
The analysis of the information arising from the sensors is complex, having regard to the spatial geometry which requires large computational capabilities. Additionally, the slaving of a system of this type may exhibit aspects that are limiting in terms of fastness of the computation time and may therefore affect the accuracy of the systems. To attain the required accuracy, the sensor, of camera type, must have a high resolution and the processing of the sensor information is subject to a prediction of the position of the LEDs and an analysis of zones of interest.
Variants of these systems exist, notably devices for detecting the shadow of a grid illuminated by a helmet-mounted source. These systems exhibit a limitation on the accurate determination of the orientation of the object to be identified.
The process of detecting the position and orientation of an object, through the observation of a pattern on said object by cameras, is less accurate. This process requires large computational capabilities and poses problems of use in disturbed environments. One way of improving the performance of such a system is to multiply the sensors and to place them in an optimal manner. This solution nevertheless remains difficult to implement.
In a general manner, the current solutions for detecting the position and orientation of an object in space, in the aeronautical field, exhibit limitations related to the compromise between the implementation of computationally extremely unwieldy solutions and the accuracy requirements demanded. Additionally, the constraints of the aeronautical environment necessitate a redundancy of the optical means or of the sensors and do not allow the implementation of simple technical solutions.